Reduction starts.
Current diff:
	<null, a>
	<null, ++>
	<null, ;>
	<null, b>
	<null, -->
	<null, ;>
Reducer ListDiffDdmin ends.
Current diff:
	<null, a>
	<null, ++>
	<null, ;>
Reduction ends.
Current diff:
	<null, a>
	<null, ++>
	<null, ;>
